Can someone please help me with part b and how we got to divide the 800,000 by 4? I need help and I am really stuck. Help is greatly appreciated

Tri-City Manufacturing expects to spend $800,000 in 2019 in appraisal costs if it does not change its incoming materials inspection method. If it decides to implement a new receiving method, it will save $80,000 in fixed appraisal costs and variable costs of $0.40 per unit of input material. The new method involves $120,000 in training costs and an additional $160,000 in annual equipment rental. It takes four units of material for each finished product. Internal failure costs an average of $160 per failed unit of finished goods. During 2019, 5% of all completed items had to be reworked. External failure costs an average of $400 per failed unit. The company's average external failures are 1% of units sold. The company carries no ending inventories, because all jobs are on a per order basis and a just-in-time inventory ordering method is used. Required: a. What is the net effect on appraisal costs for 2019, assuming the new receiving method is implemented and that 800,000 material units are received? b. How much will internal failure costs change, assuming 800,000 units of materials are received, and that the new receiving method reduces the amount of UNACCEPTABLE product units in the manufacturing process by 10%? X b. Solution part b Internal failure costs [(800,000/4) > 0.05 * $160 10% reduction from new method Savings $1,600,000 x 0.10 $ 160.000